The III-nitride semiconductor materials are known for their wide band gap property. For example, the GaN has the band gap of 3.4 eV, and the AlN has the band gap over 6.0 eV. This property is advantageous for the application in high-power and high-frequency MMIC (Monolithic Microwave Integrated Circuit), such as a high-power switch or a microwave power amplifier. A III-nitride semiconductor MMIC may include plural III-nitride semiconductor FETs. In a common layout, the gate contact layer of the plural III-nitride semiconductor FETs are formed in a comb-shape with plural gate contact fingers on a conductive area of the III-nitride semiconductor and a gate connection line connecting all gate contact fingers on the non-conductive area. The gate connection line is further connected to a gate contact pad through connection metal lines for input control voltage to the gate electrodes.
In a conventional III-nitride MMIC, the gate contact fingers form Schottky contact with the III-nitride semiconductor on the conductive area, and the gate anchor is formed on the non-conductive area or on the dielectric with a small piece metal. However, in the conventional III-nitride MMIC, the stability has a large variation, especially under high voltage and high temperature operation. The device performance at high temperature and high voltage is also related to the quality of gate adhesion to the semiconductor. When the quality of the gate adhesion to the semiconductor is poor, the end of the gate contact finger may peel off at high temperature and high voltage which decreases the Schottky stability of the device and leads to a degraded device performance. To achieve a better high temperature and high voltage application, the Schottky stability and gate adhesion of the III-nitride MMIC should be improved.